Why do Galaxies Spiral?
Current models of galactic spiral arm formation downplay a critical force - the stretching created by tidal disruption. I am convinced that someday astronomers will show that tides are a key trigger, if not the primary motivator, of galaxy spiral arm formation.
In the meantime, enjoy the images we've obtained here at the Lazar Observatory. The evidence is in plain sight, if you know where to look.
Pop quiz: Why are the outer spiral arms bluer than the inner ones?